1. Field of the Invention
The present invention relates to a decoding apparatus for decoding code data generated by an encoding process. More specifically, the present invention relates to a decoding apparatus for decoding code data generated by an encoding process including quantization of data by dequantizing the code data.
2. Description of the Related Art
Since images, audios or the like have enormous amount of data, it is common to maintain or transmit the data with the amount of data reduced by compressing it. For example, the amount of multi-value image data generated when color manuscripts or photographs are transformed into an electronic form by a scanner or when scenery or the like is photographed by a digital camera can be significantly reduced by compressing the data using a lossy coding process such as JPEG, JPEG200 or the like.
However, this lossy coding process has a problem with coding distortion. In particular, the JPEG process has a problem in that block distortion occurs at DCT block boundaries of decoded images (coding distortion).
For example, JP-A-5-014735 discloses a method in which a low pass filter is provided only at a boundary between DCT (discrete cosine transform) blocks.
JP-A-5-316361 discloses a method in which it is determined whether or not edges are present in an image, and, based on a result of the determination, a filter to be provided is selected.
JP-A-7-336684 discloses a method in which noises are added to DCT coefficients when it is determined that distortion is noticeable in a region.
A JPEG standard is disclosed in a document “ITU-T Recommendation T.81”.
A JPEG2000 standard is disclosed in a document “ITU-T Recommendation T.800”.
A method in which images having more similar textures are synthesized by adjusting distribution of frequency of transform coefficients, is disclosed in a document “D. Heeger and J. Bergen, “Pyramid based texture analysis/synthesis,” Computer Graphics, pp. 229-238, SIGGRAPH 95, 1995”.